The mechanism of action of nucleoside antimetabolites will be assessed in human tumor cells in tissue culture, and will include studies of ribosomal RNA processing, transcription, methylation of RNA and DNA and cellular oncogene expreession. These studies will deal with the cyclopentenyl analogs of adenosine (neplanoncin-A), cytidine, uridine, 3-deazaadenosine 5-fluorouridine and 5-azacytidine. The activity of these drugs will be assessed by the clonogenic survival of human colon carcinoma cell line HT-29 and the differentiation response of human promyelocytic leukemia cell line HL-60.